Synthesis and characterization of two new halo complexes of iodine:

(C4H9)4N[I2Br]7

and (C4H9)4N[I2Cl]7

and theoretical calculations of

their structures

Shahriar Ghammamya,b*, Zhila Anvarniaa, Mahnaz Jafarib, Kheyrollah Mehrania,Hossein Tavakolc, Zahra Javanshira and Gholamreza Rezaeibehbahanib

aFaculty of Science, Department of Chemistry, Islamic Azad University, Ardabil Branch,Ardabil, Iran; bFaculty of Science, Department of Chemistry, Imam Khomeini International

University, Ghazvin, Iran; cFaculty of Science, Department of Chemistry, University of Zabol,Zabol, Iran

(Received 6 August 2009; final version received 30 September 2009)

Two new compounds of iodine: (C4H9)4N[I2Br], (C4H9)4N[I2Cl], were easilysynthesized in a nearly quantitative yield using a direct reaction of I2 withtetrabutylammonium halide salts (chloride and bromide). The products wereseparated and characterized by elemental analysis and spectroscopic methodssuch as: IR, UV/Visible, 1H-NMR, 13C-NMR and 81Br-NMR techniques. Theywere studied computationally at B3LYP/LANL2DZ level of theory. Theoptimized structures are in good agreement with the available experimentalresults. Production of these compounds shows the ability of tetrabutylammoniumsalts in halide addition to main group elements.

Keywords: synthesis; halo compounds; main elements; diiodate; characterization

1. Introduction

There is a growing interest in the study of main group halo compounds [1]. Theunique properties of halide impart an unusual reactivity, which can be exploited inpreparative inorganic chemistry or in catalysis. In recent years, there has been a greatdeal of interest in the halo compounds. This is because of the important prerequisitesof a halo compound such as its mildness, versatility, selectivity, and operationalsimplicity [2]. The main reaction for this manuscript halo compounds synthesis is thereaction of tetrabutylammonium bromide or tetrabutylammonium chloride with I2.By using these type of reagents many halo compounds of main group elements canbe produced such as: (CH3)4N[PF4] [3], (CH3)4N[SeF5], (C4H9)4N[PbCl2F],(C4H9)4N[PbI2F] [4], (CH3)4N[IF8] [5], and in fewer amounts some transition metalfluorocomplexes were synthesized like (CH3)4N[MoO3F] [6], (CH3)4N[CrO3F] [7],(CH3)4N[MoF7], (CH3)4N[WF7], (CH3)4N[ReOF6] [8], and (CH3)4N[WO3F] [9].There were two primary incentives for the selection of tetraalkylammonium

*Corresponding author. Email: shghamami@ikiu.ac.ir; shghamamy@yahoo.com

Main Group Chemistry

Vol. 8, No. 4, December 2009, 299–306

ISSN 1024-1221 print/ISSN 1745-1167 online

� 2009 Taylor & Francis

DOI: 10.1080/10241220903377481

http://www.informaworld.com

(R7)4Nþ as the counter ion. Firstly, quaternary ions, such as tetrabutylammonium,

are often used as phase transfer catalysts. Secondly, they are also used as crystalgrowing agents [10–12].

2. Experimental

2.1. General

Acetonitrile (Fluka, P.A.) was distilled several times from phosphorus pentaoxidebefore using, thereby reducing its water content to 54 ppm. Tetrabutylammoniumbromide and tetrabutylammonium chloride were bought from Merck (99%). I2(Merck, P.A., 99.5%) was used without further purification. Solvents were purifiedby standard methods. Infrared spectra were recorded as KBr disks on a Shimadzumodel 420 spectrophotometer. The UV/Visible measurements were made on aUnicom model 922 spectrometer. 1H-NMR and 81Br-NMR were recorded on aBruker AVANCE DRX 500 spectrometer. All the chemical shifts are quoted in ppmusing the high-frequency positive convention. The percent compositions of elementswere obtained from the Microanalytical Laboratories, Department of Chemistry,OIRC, Tehran.

2.2. Synthesis of tetrabutylammonium brominediiodide, (C4H9)4N[I2Br],(TBABDI) (1)

Solid powder tetramethylammonium bromide (0.35 g, 1.1 mmol) was added to asolution of I2 (0.25 g, 1 mmol) in MeCN under stirring at room temperature until anorange solid precipitate was formed. Stirring was continued for 3 h, the mixture wasfiltered, washed with ether, and dried at room temperature. 1H-NMR (500 MHz,CD3CN): d ¼ 1.22 (t, 3H, ��CH3), d ¼ 1.6 (m, 4H, ��CH2��CH2��), d ¼ 2.7(t,2H, ��CH2��), 13C-NMR (124.44 MHZ, CD3CN): d 13.71, 19.76, 24.21, 59.06. Mp478C (dec.). Anal. Calc. for C16H36BrI2N: C, 33.27; H, 6.23; N, 2.42. Found: C,33.46; H, 6.25; N, 2.43%. UV/Visible, IR, were all consistent with the TBABDIstructure.

2.3. Synthesis of tetrabutylammonium chlorinediiodide, (C4H9)4N[I2Cl],(TBACDI) (2)

Tetrabutylammonium chlorinediiodate, [(C4H9)4N][I2Cl], was prepared by dissol-ving I2 (0.25 g, 1 mmol) in MeCN and adding this solution to a solution oftetrabutylammonium chloride (0.30 g, 1.1 mmol) in MeCN under stirring at roomtemperature until a red precipitate was formed. After 24 h stirring, the mixture wasfiltered, washed with ether, and dried at room temperature. Mp: 468C forC16H36ClI2N: C, 36.12; H, 6.77; N, 2.63; % found C, 36.28; H, 6.79; N, 2.64; A0.001 mol solution conductivity is 118 O71 cm2 mol71. UV/Visible, IR, 1H-NMR,and 13C-NMR were all consistent with the TBACDI structure.

3. Results and discussion

The (C4H9)4N[I2Br], tetrabutylammonium brominediiodide, TBABDI was obtainedby the reaction of (C4H9)4NBr with I2 in the acetonitrile solvent (Reaction (1)).

300 S. Ghammamy et al.

Similar reaction with (C4H9)4NCl gave (C4H9)4N[I2Cl], tetrabutylammoniumchlorinediiodide, TBACDI (Reaction (2)).

ðC4H9Þ4NBrþ I2 ! ðC4H9Þ4N½I2Br� ð1Þ

ðC4H9Þ4NClþ I2 ! ðC4H9Þ4N½I2Cl� ð2Þ

The advantages of the new method are the following: (a) There is no side product,(b) the reaction is quite fast, (c) mild conditions, and (d) the accompanied colorchange, which provides visual means for ascertaining the progress of the reaction.

In the vibrational spectra of (C4H9)4N[I2Br] and (C4H9)4N[I2Cl] complexes, theknown bands of cation were seen that confirmed with the literature data (Tables 1and 2).

For more clear characterization of the title compounds, they were studiedcomputationally at B3LYP/LANL2DZ level of theory. The optimized structures ofcomputed molecules are shown in Figure 1. Furthermore, calculated molecularparameters and some of the most important vibrational frequencies extracted fromthe output of calculations are depicted in Tables 3 and 4, respectively and nocorrected graphical representation of IR spectra for cationic and anionic parts ofprepared molecules are shown in Figure 2.

The results of the calculations from the above tables show that the structures ofthese two halodiiodate salts are not formed in dimer, trimer, or more multi-nuclearstructures in solid states.

As found and shown in Figure 1, the structures of [I2Cl]7 and [I2Br]

7 anions arelinear, that may be confirmed by structural theories such valence shell electron pair

Table 1. The frequencies (cm71) and assignment of cation and anion of (C4H9)4N[I2Br].

u (cm71) Vibration Intensity

(C4H9)4Nþ

3432 nCH2 þ n19 (w,br)3315 nCH2 þ n8 (w,br)3225 nCH2, asym.str (sh)3010 n13, nCH2, asym.str (w,br)2955 n14, CH2, asym.str (s)2864 n14 CH2, asym.str (s)2765 n7 þ n16 (w)2358 n3 þ n8 þ n16 (w)1950 n8 þ n15 (w,br)1466 n15, CH2, asym.def (w)1370 n16, CH2, sym.str (w)1151 nrock, CH2, rokingn14 (w)1022 n18, NC4, asym.str (w,br)463 n19, NC4, def. (ms)453 n19, NC4, def. (ms)

[I2Br]7 (Literature base)

I��I��Br 84I��I 117I��Br 168

Main Group Chemistry 301

repulsion (VSEPR) theory. On the basis of VSEPR theory, these anions belong tofive coordinated categories in that three lone pairs (LP) are found and abbreviated asAB2(LP)3. In this subcategory, the lone pairs occupied the equatorial positions and Batoms (one I and one Cl or Br) occupied the axial positions, which provided thelinear structure.

Electronic spectrum of (C4H9)4N[I2Br] shows two absorptions at 267 nm(e ¼ 896 mol71 l cm71) and 361 nm (e ¼ 121 mol71 l cm71). Electronic spectrumof (C4H9)4N[I2Cl] shows three absorptions at 264 nm (e ¼ 1494 mol71 l cm71),285 nm (e ¼ 1617 mol71 l cm71), 362 nm (e ¼ 598 mol71 l cm71). Tables 5 and 6

Table 2. The frequencies (cm71) and assignment of cation and anion of (C4H9)4N[I2Cl].

u (cm71) Vibration Intensity

(C4H9)4Nþ

3742 nCH2 þ n19 (w,br)3424 nCH2 þ n8 (w,br)3225 nCH2, asym.str (sh)3010 n13, nCH2, asym.str (w,br)2955 n14, CH2, asym.str (s)2865 n14 CH2, asym.str (s)2765 n7 þ n16 (w)2360 n3 þ n8 þ n16 (w)1950 n8 þ n15 (w,br)1464 n15, CH2, asym.def (w)1372 n16, CH2, sym.str (w)1154 nrock,CH2, rokingn14 (w)1021 n18, NC4, asym.str (w,br)463 n19, NC4, def. (ms)453 n19, NC4, def. (ms)

[I2Cl]7 (Literature base)

I�� I��Cl 269I��I 127I��Cl 226

Figure 1. The calculated structures for (C4H9)4N[I2Br]7 and (C4H9)4N[I2Cl]

7.

302 S. Ghammamy et al.

Table

3.

Calculatedmolecularparametersof(C

4H

9) 4N[I2Cl]and(C

4H

9) 4N[I2Br].

I 2Cl7

C2��N1��C3

104.5

H51��C33��H53

107.7

C9��C5��H17

108.2

C3��N1��C2��C6

169.4

H13��C3��C7��H25

178.6

I��I

3.14

C2��N1��C4

106.7

C8��C20��H38

109.5

H16��C5��H17

107.8

C5��N1��C3��C7

786.1

N1��C4��C8��C20

179.8

I��Cl

2.74

C2��N1��C5

107.3

C7��C3��H13

108.2

C2��C6��C18

109.7

C2��N1��C4��C8

159.1

H14��C4��C8��H27

763.0

Cl��

I��I

180.0

C3��N1��C4

112.0

H12��C3��H13

107.7

C19��C31��H47

111.3

C4��N1��C2��C6

771.8

H15��C4��C8��C20

759.9

I 2Br7

C4��C8��H26

110.5

N1��C4��C8

118.9

C2��C6��H23

111.6

C3��N1��C4��C8

787.1

C3��C7��C19��H37

56.4

I��I

3.14

C4��N1��C5

113.5

C31��C19��H37

109.4

C18��C6��H22

108.5

C5��N1��C4��C8

41.1

H24��C7��C19��C31

57.4

I��Br

2.93

N1��C2��C6

117.4

N1��C4��H15

105.6

H46��C31��H47

108.0

C5��N1��C2��C6

50.3

H26��C8��C20��H39

764.3

Br��

I��I

180.0

N1��C2��H10

105.4

C8��C4��H14

110.5

H22��C6��H23

107.3

C2��N1��C5��C9

157.4

H27��C8��C20��C32

759.5

Bu4Nþ

(forboth)

H26��C8��H27

107.6

C9��C21��H40

109.6

C3��C7��C19

109.3

H10��C2��C6��H23

763.2

H29��C9��C21��H41

179.3

N1��C2

1.57

C6��C2��H10

109.9

H14��C4��H15

107.7

C20��C32��H50

111.3

C2��N1��C3��C7

158.0

C6��C18��C30��H42

179.9

N1��C3

1.56

C7��C19��C31

112.0

N1��C5��C9

119.0

H49��C32��H50

108.0

C4��N1��C5��H17

153.7

C7��C19��C31��H47

60.1

N1��C4

1.55

H10��C2��H11

108.2

H42��C30��H44

107.7

C19��C7��H24

108.4

N1��C2��C6��C18

177.5

H36��C19��C31��H45

58.2

C��C

(all)

1.54

N1��C3��C7

119.2

N1��C5��H17

105.1

C21��C33��H52

111.3

C4��N1��C3��C7

42.8

C9��C21��C33��H53

60.1

C��H

(all)

1.10

N1��C3��H12

105.5

C9��C5��H16

110.2

H24��C7��H25

107.6

H11��C2��C6��C18

761.9

H40��C21��C33��H51

58.2

Molecularparameters.Bondlengthsare

inAngstromsandanglesare

indegrees.

Main Group Chemistry 303

show the electronic transitions data of these two halodiiodate compounds,respectively. 1H-NMR and 13C-NMR cationic signals were seen [13].

In the 81Br-NMR of (C4H9)4N[I2Br], a signal is seen in the 763 ppm thatconfirmed the bonding of bromide and iodine atoms.

3.1. Computational methods

Density functional theory (DFT) has been widely applied by chemists to study theelectronic structure of molecules in the past 30 years [14,15]. In this work, all

Table 4. Some of the most important theoretical frequencies (corrected, in cm71) of cationand anion of (C4H9)4N[I2Cl] and (C4H9)4N[I2Br].

I2Cl7 Bu4N

þ (for both molecules)

70 Bending (2) 3011 n13, nCH2, asym.str 1156 nrock, CH2, rocking n14116 I��I stretching 2959 n14, CH2, asym.str 1010 n18, NC4, asym.str223 I��Cl stretching 2765 n7 þ n16 934 Bending

I2Br7 2358 n3 þ n8 þ n16 784 Bending

53 Bending (2) 1950 n8 þ n15 508 Bending106 I��I stretching 1479 n15, CH2, asym.def 481 Bending159 I��Br stretching 1372 n16, CH2, sym.str 419 Bending

Table 5. Transitions specifications of TBABDI.

l2(e, M71 cm71) l1(e, M

71 cm71)

361 (121) 267 (896)

Figure 2. Graphical representation of IR spectra (no corrected) for each part of preparedmolecules.

Table 6. Transitions specifications of TBACDI.

l3 (e, M71 cm71) l2 (e, M

71 cm71) l1 (e, M71 cm71)

362 (598) 285 (1617) 264 (1494)

304 S. Ghammamy et al.

calculations have been carried out at the B3LYP/LANL2DZ level of theoryemploying the Gaussian 03 program package [16]. The absence of the imaginaryfrequency verified that the structures were true minima at their respective levels oftheory for each molecule. Furthermore, frequency calculations were performed atthe same level on the respective fully optimized geometries to obtain the vibrationalspectra. Results of frequency calculations were used after applying appropriatescaling factor [17].

4. Conclusion

Two tetrabutylammonium salts with [I2Br]7, [I2Cl]

7 anions were synthesized in one-step reaction and characterized by elemental analysis, IR, UV/Visible, and 13C-NMR, 1H-NMR, and 81Br-NMR techniques. The optimized geometrical parameterscalculated at B3LYP/LANL2DZ level. The optimized structures are in goodagreement with the available experimental results. In the present article, the infraredspectra of the iodo halide complexes were studied using the theoretical andexperimental methods. Electronic and vibration spectra of these new bromo andchloro compounds were studied. Production of these compounds shows the ability oftetrabutylammonium bromide and tetrabutylammonium chloride in bromide andchloride addition to main group elements.

Acknowledgment

The authors thank Dr. Mahjoub for valuable discussions.

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